The present invention generally relates to optical recording/reproducing systems, and in particular to an optical assembly of an optical recording/reproducing apparatus recording and/or reproducing an information signal on and from both sides of a disk-shaped information recording medium by means of an optical beam for focusing the optical beam on the recording medium.
Generally, conventional optical disk recording/reproducing apparatus records and/or reproduces an information signal on and from one side of a disk-shaped recording medium (referred to hereinafter as a disk) by means of an optical recording/reproducing system. Such an optical recording/reproducing system comprises a light source, an optical assembly for focusing an optical beam, focusing and tracking mechanisms for controlling the optical beam, and a light detecting element. The optical recording/reproducing system is sometimes referred to as an optical head and radiates an optical beam on the disk and receives the optical beam reflected back from the disk. In such a disk, it is naturally desirable that the both sides of the disk can be used for storage of the information signal so that the recording capacity per one disk is increased.
In order to enable the recording and reproducing of the information signal on and from the both sides of the disk, one may use a well known automatic turn-over mechanism which turns the disk upside down while using a single optical head for focusing the optical beam on the lower side of the disk, for example. However, such automatic turn-over mechanism is complex and occupies a large space not only due to the mechanism itself but also due to the movement of the disk at the time of turn-over. Therefore, the optical disk recording and reproducing apparatus using such automatic turn-over mechanism inevitably becomes bulky and complex.
Also, there is a known optical disk recording apparatus for recording an optical information signal on both sides of an optical disk according to the Laid-open Japanese Patent Application No. 54-35707, in which a pair of optical recording systems are provided on both sides of the disk for recording the information signal on the both sides of the disk. In this conventional recording apparatus, two bulky and heavy optical recording systems have to be used and therefore the apparatus inevitably becomes large and heavy. Further, the optical recording and reproducing apparatus using the construction as disclosed by the Laid-open Japanese Patent Application No. 54-35707 has a problem that a large access time is required for the optical recording/reproducing system to move to a desired track position due to the inertia of the optical recording/reproducing system.